Method and apparatus for vibration casting of vehicle wheels

ABSTRACT

A vehicle wheel mold is vibrated at a frequency within a range of 0.1 to 10,000 Hz during a casting process. The vibration reduces the solidification time needed to form a wheel casting while improving the tensile strength of the wheel.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a Continuation-in Part of U.S. patentapplication Ser. No. 09/760,074, filed on Jan. 12, 2001, which claimspriority from International Application No. PCT/US99/15,719 filed onJul. 12, 1999, which claims the benefit of U.S. Provisional ApplicationNo. 60/092,684, filed on Jul. 13, 1998. The disclosures of all three ofthe above applications are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTINGCOMPACT DISC APPENDIX

[0003] Not Applicable

BACKGROUND OF THE INVENTION

[0004] This invention relates in general to casting of vehicle wheelsand in particular to a method and apparatus for vibration casting ofvehicle wheels.

[0005] Vehicle wheels include a circular wheel disc attached to anannular wheel rim. The wheel disc includes a central wheel hub having apilot hole and plurality of wheel mounting holes formed therethrough. Aplurality of equally circumferentially spaced radially extending spokessupport the wheel hub within the wheel rim. The wheel rim is adapted tosupport a pneumatic tire.

[0006] In the past, vehicle wheels typically have been formed entirelyfrom steel. However, one piece wheels formed entirely from light weightmetals, such as aluminum, magnesium and titanium or alloys thereof, arebecoming increasingly popular. In addition to weighing less thanconventional all-steel wheels, such light weight wheels can bemanufactured having a pleasing esthetic shape. Weight savings also canbe achieved with two piece wheels formed by attaching a light weightmetal alloy wheel disc to a steel wheel rim.

[0007] Light weight wheels are typically formed by forging or castingoperations. During a forging operation, a heated billet of the lightweight metal alloy is squeezed by very high pressure between successivesets of dies until the final shape of the wheel is formed. During acasting operation, molten metal is poured or forced under pressure intoa cavity formed in a multi-piece wheel mold. After the metal coolssufficiently to solidify, the mold is opened and a rough wheel castingis removed. The wheel casting is then machined to a final shape.Machining can include turning the outside and inside surfaces of thewheel rim, facing the inboard and outboard wheel disc surfaces anddrilling the center pilot hole and the mounting holes through the wheelhub.

[0008] Conventional casting operations include numerous processes, suchas die casting, low pressure injection casting and gravity casting.Conventional casting operations typically utilize a wheel mold formedfrom a number of movable segments which are opened to allow removable ofthe wheel casting from the mold. Referring now to the drawings, there isillustrated in FIG. 1, generally at 10, a typical multi-segment wheelmold used for gravity casting. The mold 10 includes a base segment 11which supports a plurality of movable side segments 12, two of which areshown in FIG. 1. The side segments 12 can be retracted and extended in ahorizontal direction by a conventional mechanism 13. A movable top core14 extends between the side segments 12. The top core 14 can be raisedand lowered in a vertical direction by the mechanism 13. When the mold10 is closed, the top core 14 cooperates with the side and base segments12 and 11 to define a wheel mold cavity 15. The outline of a finishedvehicle wheel cast in the mold 10 is illustrated in FIG. 1 by the dashedline labeled 16.

[0009] For high volume production of castings, such as vehicle wheels, ahighly automated gravity casting process is frequently used. Suchautomated gravity casting processes typically use a casting machinehaving a plurality of multi-segment molds mounted upon a movingstructure, such as a rotatable carousel. Each mold is indexed past arefractory furnace containing a pool of molten metal. A charge of moltenmetal is poured into a gate formed in the mold which communicates withthe mold cavity. Gravity causes the metal to flow from the gate into themold cavity. The mold and the molten metal cool as the casting machineindexes the other molds to the refractory furnace for charging withmolten metal. After a sufficient cooling time has elapsed for the moltenmetal to solidify, the mold is opened and the wheel casting removed. Themold is then closed and again indexed to the refractory furnace to berefilled with another charge of molten metal.

BRIEF SUMMARY OF THE INVENTION

[0010] This invention relates to a method and apparatus for vibrationcasting of vehicle wheels. As explained above, casting of vehicle wheelsis a highly automated process. However, the production of a castingmachine is constrained by the length of time required for the moltenmetal to solidify within the individual wheel molds. A reduction in thelength of time needed for the molten metal to solidify would allow anincrease in the speed of operation of the casting machine, therebyincreasing the number of wheels produced in a given time period.Accordingly, it would be desirable to reduce the length of time neededfor the molten metal to solidify.

[0011] The present invention contemplates an apparatus for casting avehicle wheel component which includes a multi-segment mold for thevehicle wheel component and a device for vibrating a portion of themold. In the preferred embodiment, the device for vibrating includes apneumatically powered ball vibrator. The ball vibrator is mountedadjacent to the mold and is operable to vibrate a top core of the mold.The wheel component can be either a one piece vehicle wheel or a fullface wheel disc.

[0012] Alternately, the device for vibrating can be a pneumaticallypowered reciprocating hammer or an electrically powered device. Theinvention contemplates vibrating the mold at a frequency within therange of 0.1 Hz to 10,000 Hz. Additionally, the vibration frequency maybe varied as a function of time. The invention also contemplatesmounting an manifold upon the mold for injection of an inert gas intothe mold cavity after the cavity is charged with molten metal. In thepreferred embodiment, helium is used as the inert gas.

[0013] The invention also contemplates a method for forming a vehiclewheel component which includes providing a multi-segment mold forcasting the wheel component and a device for vibrating a portion of thewheel mold. The cavity of the wheel component mold is filled with acharge of molten metal. A portion of the wheel component mold isvibrated at a frequency within the range of 0.1 Hz to 10,000 Hz whilethe molten metal solidifies. The wheel component casting is then removedfrom the mold. The molten metal can be poured into the mold cavity withgravity causing the molten metal to flow throughout the mold cavity orforced under pressure into the mold cavity with the pressure causing themolten metal to flow throughout the mold cavity. The invention alsocontemplates injecting an inert gas into the mold cavity as the moltenmetal cools. Additionally, the vibration can be started either before orafter the mold cavity is charged with the molten metal.

[0014] Various objects and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the preferred embodiment, when read in light of theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a sectional view of a multi-segment vehicle wheel moldaccording to the prior art.

[0016]FIG. 2 is a sectional view of a multi-segment vehicle wheel moldin accordance with the invention.

[0017]FIG. 3 is a sectional view of the multi-segment vehicle wheel moldshown in FIG. 2 equipped with an alternate embodiment of the invention.

[0018]FIG. 4 is a sectional view of the multi-segment vehicle wheel moldshown in FIG. 2 equipped with another alternate embodiment of theinvention.

[0019]FIG. 5 is a flow chart for a method for casting a vehicle wheel inaccordance with the invention.

[0020]FIG. 6 is a flow chart for an alternate embodiment of the methodfor casting a vehicle wheel shown in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] The inventor has determined that vibrating a wheel mold cansignificantly reduce the amount of time needed for the molten metalcontained within the mold cavity to solidify. Referring again to thedrawings, there is illustrated in FIG. 2 a multi-segment wheel mold 20used for gravity casting of wheels which is in accordance with thepresent invention. Components of the mold 20 which are similar tocomponents shown in FIG. 1 have the same numerical designators. As shownin FIG. 2, a conventional commercially available ball vibrator 21 ismounted upon the mold top core 14. The vibrator 21 is secured to the topcore 14 by a plurality of threaded fasteners 22. In the preferredembodiment, the vibrator 21 selected has a base which fits upon the topcore 14 to minimize installation effort and time.

[0022] In the preferred embodiment, the vibrator 21 is operated bycompressed air supplied though an air line 23; however, the inventionalso can be practiced with ball vibrators operated by other mediums,such as a hydraulically powered vibrator, or the vibrator can be poweredby an electric motor. For the vibrator 21 shown, compressed air forces achrome steel ball around bearing grade races to impart vibratory energythrough the top core 14 to the molten metal contained in the mold cavity15.

[0023] The compressed air, which is not affected by the hightemperatures encountered in a foundry, can be supplied from a readilyavailable source, such as tapping into the foundry air supply. Thecompressed air flows though a regulator (not shown) for controlling thepressure to adjust the speed and force of the vibrator. In the preferredembodiment, the air pressure is adjustable over range of from 60 poundsper square inch (psi) to 100 psi.

[0024] The compressed air also flows through either a manual valve or asolenoid valve (not shown) which is connected between the regulator andthe vibrator 21. The valve controls the operation of the vibrator 21. Inthe preferred embodiment, a solenoid valve is utilized with the valvecoil connected to a microprocessor which controls the casting machine.This assures that the vibrator 21 is actuated during the appropriateperiods in the cycle. A filter (not shown) also is included in the airsupply to remove an contaminants from the supplied air which may damagethe vibrator 21. The compressed air is vented from the vibrator 21through an exhaust port 24. An optional muffler (not shown) can beattached to the exhaust port 24 to reduce the noise generated by thedischarge of the compressed air.

[0025] The inventors have found that vibration of the mold 20 while themolten metal contained therein solidifies has significantly reduced thesolidification time for a wheel casting. The cooling of the molten metalis accelerated as the vibration of the mold increases contact betweenthe molten metal and the steel mold segments. During tests, thesolidification time has been reduced from six minutes without vibrationto 4 to 5 minutes. Thus, vibration can reduce solidification time by 20to 33 percent. Additionally, the inventor has observed that, withvibration, the microstructure grain size of a wheel casting is reducedfrom the size resulting without vibration. Also, the dendrite armswithin the casting are broken off while the spacing of the dendrite armswithin the casting is reduced when the mold is vibrated while the metalsolidifies. Accordingly, the tensile and other mechanical strength ofthe wheel is improved by the application of vibration.

[0026] An alternate embodiment of the invention is illustrated by themold 30 shown in FIG. 3. As before, components of the mold 30 which aresimilar to components shown in FIG. 1 have the same numericaldesignators. As shown in FIG. 3, a conventional pneumatic knock outhammer 31 is mounted adjacent to the mold top core 14. The hammer 31 isheld in position by a mounting bracket (not shown) which is attached tothe mold support mechanism 13. The hammer is 31 actuated by compressedair supplied through an air line 32. Similar to the ball vibrator 21described above, the compressed air is vented through an exhaust port(not shown). The hammer 31 has a reciprocating head 33 which is locatedadjacent to a top plate 34 of the mold top core 14. When actuated, thehammer head 33 taps the top plate 34 to impart vibrations through thetop core 14 to the molten metal contained within the mold cavity 15.Operation of the hammer 31 produces results similar to those describedabove for the ball vibrator 21.

[0027] While the preferred embodiments of the invention have beenillustrated and described above for a ball vibrator 21 and a knock outhammer 31, it will be appreciated that the invention also can bepracticed with other conventional devices for imparting vibrations tothe wheel mold 10. For example, electrically operated vibrator 35, asillustrated in FIG. 4, may be mounted upon the mold top plate 34. Asshown in FIG. 4, the electric vibrator 35 receives power from anoscillator 36. The oscillator 36 is connected through a switch 37 to apower supply 38. In the preferred embodiment, the timer and oscillatorfrequency are controlled by a control unit 39, that also receives energyfrom the power supply 38. In the preferred embodiment, the control 39activates the electric vibrator 35 at a predetermined time in thecasting operation and, as will be described below, times a vibrationcycle with the vibrator 35 being deactivated after a predetermined timeperiod T₁ passes. The oscillator frequency is adjusted for theparticular mold and metal being cast. While an oscillator with anadjustable frequency is shown in FIG. 4, it will be appreciated that theinvention also may be practiced with a fixed frequency oscillator (notshown). The invention also contemplates that similar control equipment(not shown) is utilized with the ball vibrator 21 and knock out hammer31 described above.

[0028] Additionally, while gravity casting has been shown and describedabove, it will be appreciated that the invention also can be practicedwith other conventional casting processes, such as, for example, lowpressure and die casting.

[0029] The invention contemplates that the mold is vibrated at afrequency within the range of 0.1 Hz to 10,000 Hz. Preferably, the moldis vibrated at a frequency within the range of 10 Hz to 1,000 Hz, orwithin the range of 10 Hz to 500 Hz. Additionally, the inventioncontemplates varying the vibration frequency as a function of time. Forexample, the vibration may commence at 1,000 Hz and be reduced to 10 Hzas the molten metal solidifies. The frequency reduction may be either alinear or non-linear function of time.

[0030] The present invention also contemplates enhancing the castingprocess by injecting an inert gas into the mold cavity after the cavityhas been charged with molten metal. In the preferred embodiment, heliumis used; however, other inert gases also may be utilized. The gasdisplaces any air that may remain between the metal and the moldsegments to increase conduction of heat from the molten metal to themold segments, thereby further decreasing the cooling time for thecasting. As the mold cavity is charged, the molten metal displaces aircontained within the cavity through vents provided in the mold. Thevents are sized sufficiently small to prevent molten metal from enteringthe vents and thereby plugging them upon solidification. Therefore, theinvention also contemplates mounting a manifold 40 upon the mold that isin communication with the air vents, as illustrated in FIG. 4. Inert gasis supplied to the manifold 40 via external piping or hoses 41. Once theair has vented from the mold cavity, and an initial skin formed on thecasting, the inert gas would be admitted via the manifold and air ventsinto the mold cavity. The manifold would have valves (not shown) mountedthereupon to allow the air within the mold cavity to vent to theatmosphere as the molten metal is added. The valves would then beswitched to close the vents to the atmosphere and to receive thepressurized inert gas. Alternately, the manifold could be mounted tocommunicate with the bores holding the ejector pins with the inert gasbeing injected through the injector pin holes. Again, valves would beprovided on the vents to seal the mold from the atmosphere as the inertgas is injected. Additionally, the manifold could cover both the ventsand injector pin bores and inject the inert gas through both types ofopenings. Thus, while the manifold 40 has been shown mounted upon theupper portion of the mold 30 in FIG. 4, it will be appreciated that themanifold also may be mounted upon other portions of the mold.Additionally, the invention also contemplates mounting a similarmanifold upon molds 20 and 30 shown in FIGS. 2 and 3, respectively.

[0031] The present invention also contemplates a method for vibratorycasting of a vehicle wheel. The method is illustrated by the flow chartshown in FIG. 4. In functional block 42, a wheel mold, which is equippedwith a vibratory device, is charged with molten metal. The metal may bepoured under gravity or injected into the mold cavity by a low pressure.The vibratory device is activated and the mold vibrated in functionalblock 43. The vibration continues at a constant frequency for apredetermined time period, T₁, which is a function of the volume ofmetal being cast. Alternately, as described above, the vibrationfrequency may be varied as a function of time. In the preferredembodiment, the vibration time is between 200 and 250 seconds; however,it will be appreciated that the invention also can be practiced withother vibration time periods. For example, the vibration may continueuntil the casting is completely cooled and ready to be removed from themold (not shown). In decision block 44, it is determined whether thetime T₁ has passed. If, in decision block 44, the total vibration timeis less than T₁, the method returns to functional bock 43 and vibrationcontinues. If, in decision block 44, the total vibration time is greaterthan or equal to T₁, the method advances to functional bock 46 and thevibratory device is turned off. If the total cooling time needed for thecasting has not elapsed, the mold and casting are allowed to continue tocool for a additional time period, T₂, in functional block 48; however,as indicated, this step is optional. In functional block 50, the mold isopened and the wheel casting removed therefrom.

[0032] In the preferred embodiment, the method is be practiced withvibration being applied to the mold while the mold cavity is beingcharged with the molten metal. This enhances release of gases entrappedwithin the molten metal. A flow chart for the preferred method is shownin FIG. 5, where functional blocks that are similar to those shown inFIG. 4 have the same numerical identifiers. The method begins withactivation of the vibratory device in functional block 52. The vibrationcontinues for a predetermined time period, T₁′, which is a function ofthe volume of metal being cast and includes the time needed to chargethe mold. In the preferred embodiment, the vibration time is between 200and 250 seconds; however, as before, it will be appreciated that theinvention also can be practiced with other vibration time periods. Infunctional block 54, the wheel cavity is charged with molten metal asthe mold continues to be vibrated. The metal may be poured under gravityor injected into the mold cavity by a low pressure. Once the mold cavityis charged with molten metal, an inert gas, such as helium, is injectedinto the mold, as shown in functional block 56. As indicated in FIG. 5,such use of inert gas is optional and may be omitted from the method.Once the inert gas is added, the method advances to functional block 58where vibration of the mold continues for the remainder of thepredetermined time period T₁′. The remainder of the method is the sameas described above. Accordingly, the method advances to decision block44, where it is determined whether the time T₁′ has passed. If, indecision block 44, the total vibration time is less than T₁′, the methodreturns to functional bock 58 and vibration continues. As describedabove, the vibration applied to the mold may be at a constant frequencyor the vibration frequency may vary as a function of time. For example,one frequency may be used while the mold cavity is being charge, andanother frequency may be used as the molten metal solidifies. If, indecision block 44, the total vibration time is greater than or equal toT₁′, the method advances to functional bock 46 and the vibratory deviceis turned off. If the total cooling time needed for the casting has notelapsed, the mold and casting are allowed to continue to cool for aadditional time period, T₂, in functional block 48; however, asindicated, this step is optional. In functional block 50, the mold isopened and the wheel casting removed therefrom.

[0033] Another alternate embodiment of the method contemplates a delaybefore actuating the vibrator to allow the mold to be charged withmolten metal and for the molten metal to be begin to solidify (notshown). In the preferred embodiment, the delay is in the range of fromzero to 30 seconds; however, it will be appreciated that the inventionalso can be practiced with delays which exceed 30 seconds.

[0034] While the preferred embodiment of the invention has beenillustrated and described with vibration applied to the top core of awheel mold, it will be appreciated that the invention also can bepracticed with the vibration applied to other portions of the mold, suchas, for example, to a side segment (not shown) or to the base segment(not shown). Additionally, vibration can be applied simultaneously to aplurality of mold segments (not shown).

[0035] In accordance with the provisions of the patent statutes, theprinciple and mode of operation of this invention have been explainedand illustrated in its preferred embodiment. However, it must beunderstood that this invention may be practiced otherwise than asspecifically explained and illustrated without departing from its spiritor scope. For example, while the preferred embodiment of the inventionhas been illustrated and described for casting a one piece wheel, itwill be appreciated that the invention also can be practiced for castinga component of a vehicle wheel, such as a full face wheel disc or awheel rim.

What is claimed is:
 1. An apparatus for casting a one piece vehiclewheel comprising: a mold base segment; a plurality of movable mold sidesegments; a movable top core segment, said top core segment co-operatingwith said base and side segments to define a gravity fed mold cavity forgravity casting a vehicle wheel; and a vibration device mounted upon oneof said mold segments, said vibration device being operative toselectively vibrate said mold segment at a frequency within a range of0.1 to 10,000 Hz whereby the cooling of molten metal contained withinsaid mold cavity is accelerated and the mechanical strength theresulting cast vehicle wheel is enhanced.
 2. The apparatus according toclaim 1 wherein said vibration device is operative to selectivelyvibrate said mold segment at a frequency within a range of 1 Hz to 1,000Hz.
 3. The apparatus according to claim 2 further including a timerdevice connected to said vibration device, said timer device operativefor controlling the duration of the mold vibration.
 4. The apparatusaccording to claim 3 wherein said vibration device is pneumaticallypowered and adapted to be connected to a supply of compressed air andfurther wherein the apparatus includes a solenoid valve for controllingthe flow of compressed air into said vibration device and an adjustablepressure regulator for controlling the frequency and force of saidvibration device.
 5. The apparatus according to claim 3 wherein saidvibration device is electrically actuated.
 6. The apparatus according toclaim 5 further including a frequency controlling device connected tosaid vibration device, said frequency controlling device operative tovary the frequency of vibration as a function of time.
 7. The apparatusaccording to claim 5 further including a manifold mounted upon said moldand communicating with said mold cavity, said manifold operative toinject an inert gas into said mold cavity.
 8. The apparatus according toclaim 7 wherein said inert gas is helium.
 9. A method for forming a onepiece vehicle wheel casting comprising the steps of: (a) providing amulti-segment gravity fed mold for gravity casting the vehicle wheel,the mold having a vibration device mounted upon a segment thereof, thevibration device being selectively operable to vibrate the mold; (b)filling the cavity of the wheel mold by gravity with a charge of moltenmetal; (c) activating the vibration device to vibrate mold at afrequency within the range of 0.1 Hz to 10,000 Hz upon completion of thefilling of the mold cavity with molten metal; (d) deactivating thevibration device; (e) opening the mold; and (f) removing the wheelcasting from the mold.
 10. The method according to claim 9 furtherincluding, subsequent to step (d), allowing the metal in the mold cavityto continue to cool before the mold is opened.
 11. The method accordingto claim 10 wherein the top core is vibrated in step (c) after apredetermined time period has elapsed following the filling of the moldcavity.
 12. The method according to claim 10 wherein the vibrationdevice provided in step (a) is pneumatically powered.
 13. The methodaccording to claim 10 wherein the vibration device provided in step (a)is electrically powered.
 14. The method according to claim 10 furtherincluding a manifold mounted upon the wheel mold, the manifold incommunication with the mold cavity, and further wherein step (d)includes using the manifold to inject an inert gas into the mold cavity.15. The method according to claim 14 wherein the inert gas is helium.16. A method for forming a one piece vehicle wheel casting comprisingthe steps of: (a) providing a multi-segment gravity fed wheel mold forgravity casting the vehicle wheel, the mold having a vibration devicemounted upon a segment thereof, the vibration device being selectivelyoperable to vibrate the mold; (b) activating the vibration device tovibrate the wheel mold at a frequency within a range of 0.1 Hz to 10,000Hz; (c) filling the cavity of the wheel mold by gravity with a charge ofmolten metal; (d) continuing to vibrate the top core while the moltenmetal cools; (d) deactivating the vibration device; (e) opening themold; and (f) removing the wheel casting from the mold.
 17. The methodaccording to claim 16 further including, subsequent to step (d),allowing the metal in the mold cavity to continue to cool before themold is opened.
 18. The method according to claim 17 wherein thevibration device provided in step (a) is pneumatically powered.
 19. Themethod according to claim 17 wherein the vibration device provided instep (a) is electrically powered.
 20. The method according to claim 17further including a manifold mounted upon the wheel component mold, themanifold in communication with the mold cavity, and further wherein step(d) includes using the manifold to inject an inert gas into the moldcavity.
 21. The method according to claim 20 wherein the inert gas ishelium.